1. Field of the Invention
This invention relates to high frequency, high bit-rate, optoelectric (photonic) heterojunction devices and more particularly, to controlling the equivalent temperature of the energy distribution fraction of the mobile charge-carrier plasma and gain in the active layer of the heterojunction in order to control the electromagnetic output power.
2. Description of the Prior Art
Optoelectronic semiconductor devices that emit electronic radiation are used extensively today for applications such as, for example, fiber-optic telecommmications and laser printers. These devices include light-emitting diodes (LED) and the diode laser. Other such devices detect and modulate optical signals generated by an external radiation-emitting oscillator, while others convert optical electronic radiation into electrical energy. The theory and operation of these devices are well understood in the art as was discussed in the book "Physics of Semiconductor Lasers" by S. M. Sze, Chapter 12, p. 736, pub. by John Wiley & Sons, New York, 1981.
Furthermore, as also described in the book by Sze, Chapter 12, Sec. 12.5.1, referenced above, heterostructures with low threshold current density have been designed by the use of: "carrier confinement provided by the energy barriers of higher bandgap semiconductor surrounding the active region, etc." More recently, small, efficient quantum well optoelectronic switching devices, such as the optical modulators and switches that were described in the article entitled "Quantum Well optoelectronic Switching Devices" by D. A. B. Miller, Int. J. of High Speed Electronics, Vol. 1, No. 1, pp 19-46, March 1990, are capable of logic themselves and have potential for integration, and in the article entitled "Advances in Optoelectronic Integration" by O. Wada, Int. J. of high Speed Electronics, Vol. 1, No. 1, pp 47-71, March 1990, which reviewed the latest advances in optoelectronic integration. Furthermore, in the article entitled "Analysis of Semiconductor Microcavity Lasers Using Rate Equations" by G. Bjork and Y. Yamamoto, IEEE J. of Quantum Electronics, Vol. 27, No. 11, pp 2386-2396, Nov. 1991, equations that might achieve microcavity lasers with higher modulation speeds than previous devices were theoretically considered.
Devices for optical power modulation, such as described above, can be divided into two groups: active and passive devices. Active devices radiate electromagnetic power simultaneously with modulation and passive devices only modulate the radiation that passes through them. In all these devices, high frequency and high pulse rate modulation of optical power is the problem of importance in optical communication and high data rate system.
However, it is well known in the art that at present the maximum effective modulation bandwidth is limited to about 10 GHz for semiconductor lasers and to about 1 GHz for light diodes (Sze referenced above). Consequently, to investigate the limits on bandwidth, V. B. Gorfinkel and I. I. Filatov, in the article entitled "Heating of an Electron Gas by an hf Electric Field in the Active Region of a Semiconductor Heterolaser", Sov. Phys. Semicond., Vol. 24, No. 4, April 1990, investigated theoretically the influence of the heating of electron gas by an electric field E(t) in the heterostructure AlGaAs, GaAs, AlGaAs on the optical gain. We considered only the energy balance equation and the carrier density rate equations in order to determine theoretically the influence of electric field E(t)=E.sub.0 +E.sub.1 Sin (2.pi.ft) on the optical gain. Indeed, our theoretical analysis indicated that (where f is the applied signal frequency and t is time) depending on the ratio of the variable and constant components of the heating field E.sub.1 and E.sub.0, the optical gain value may theoretically be modulated both at signal frequency f and at double frequency 2 f up to f=400 GHz! But, this theoretical analysis (Gorfinkel & Filatov) above did not consider any actual lasing operation and did not take into account any rate equation for light. Thus, our initial theoretical analysis encouraged us to proceed further with a new analysis and, if promising, to investigate new methods that might overcome the bandwidth problems associated with the prior art.
Subsequently, as described in the article entitled "High Frequency Modulation of Quantum Well Heterostructure Diode Lasers by Carrier Heating in Microwave Electric Field" by S. A. Gurevich et al, Joint Soviet-American Workshop on the Physics of Semiconductor Lasers, p. 67, May 20-Jun. 3, 1991, our more complete theoretical analysis that considered the laser equations among others revealed that the optical gain of a quantum well heterostructure can be modulated by a spatially controlled microwave electric field when the field is applied by semiconductor contacts to the active layer. Our results were particularly surprising because Takamiza et al in Proc. IEEE, Vol. 56, No. 1, p. 135, 1968, failed in their early attempts to modulate laser output by placing samples in a microwave waveguide. Thus our method, which includes controlling the period and spatial distribution of the electric field inside the active layer, appears to have overcome the problems of the prior art.
More recently, Gorfinkel and Luryi published in Applied Physics Letters, 60 (25), 22. Jun. 1992, pp 3141-3143, an article entitled "Rapid Modulation of Interband Optical Properties of Quantum Wells by Intersubband Absorption" in which we calculated theoretically that intersubband radiation can control the mobile electron temperature and modulate the optical properties of a semiconductor quantum well. Our calculations in this article of a modulator are based on the same concepts described in the parent application relating to modulating by heating of one mobile charge carrier, but substituting intersubband radiation from a CO.sub.2 laser for heating mobile electron charge carriers.
The entire specifications of the parent application Ser. No. 07/815,174 filed on Dec. 31, 1991, are particularly incorporated herein, including the Detailed Description of the Preferred Embodiments.
Furthermore, applicants request that the prior art patents cited by the Examiner during examination of the parent application, namely U.S. Pat. No. 5,119,393, which issued to Oka on Jun. 2, 1992, and U.S. Pat. No. 5,081,633, which issued to Danner on Jan. 14, 1992, be made references of record in the present continuation-in-part. Both patents described lasers that were constructed with a plurality of optical cavities and with a plurality of electrodes. Oka teaches the use of a p-n junction to pump both types of charge carriers and Danner teaches the use of an indirect bandgap active layer and a constant electric field to transform the indirect material to direct bandgap. Thus, neither Oka nor Danner can fraction in accordance with the present invention to generate short pulses of photonic radiation by heating one type of charge carrier with a modulated electric field, as discussed below in connection with FIG. 5.